This application is related to Pulse Oximeter With Motion Detection, filed on even date herewith by Victor E. Kimball, which is incorporated here by reference.
The present invention is directed generally to medical devices and more particularly to non-invasive optical sensors for physiologic parameters such as blood oxygen saturation content.
Optical spectroscopy techniques have been developed for a wide variety of uses within the medical community. For example, pulse oximetry and capnography instruments are in widespread use at hospitals, both in the surgery suites and the post-op ICU""s. These technologies have historically been based on absorption-based spectroscopy techniques and have typically been used as trend monitors in critical care environments where it is necessary to quickly determine if a patient""s vital parameters are undergoing large physiologic changes. Given this operating environment, it has been acceptable for these devices to have somewhat relaxed precision and accuracy requirements, given the clinical need for real-time point-of-care data for patients in critical care situations.
Both pulse oximeters and capnography instruments can be labeled as non-invasive in that neither require penetration of the outer skin or tissue to make a measurement, nor do they require a blood or serum sample from the patient to custom calibrate the instrument to each individual patient. These instruments typically have pre-selected global calibration coefficients that have been determined from clinical trial results over a large patient population, and the results represent statistical averages over such variables as patient age, sex, race, and the like.
There is, however, a growing desire within the medical community for non-invasive instruments for use in such areas as the emergency room, critical care ICU""s, and trauma centers where fast and accurate data are needed for patients in potentially life threatening situations. Typically, these patients are not anesthetized and motion-induced artifacts may corrupt data from patient-attached monitoring instruments. Also, patients in shock or acute trauma may have oxygen saturation levels well below the normal physiologic range, or may suffer from reduced blood flow.
Given the situation described above there is a need for a technique to compensate for, or eliminate, motion-induced artifacts in patient-attached critical care monitoring instruments. Also, a need exists to extend the accurate operational range of patient-attached pulse oximeters in environments when the patient""s blood oxygen saturation is well below the normal physiologic range, or where there is low blood flow. Consequently, the invention is directed to improving pulse-oximetry by incorporating additional signals to aid in the triggering of the pulse-oximeter or in analyzing the data received by the pulse oximeter. This includes measuring a pulsatile characteristic of the patient at a position close to, or at the pulse-oximetry measurement site, or using pulsatile characteristics that result from contraction of the patient""s heart. One particular embodiment of the invention is directed to a method of determining hemoglobin oxygen saturation at a measurement site on a patient. The method includes detecting a first pulsatile characteristic of the patient proximate the measurement site and making hemoglobin oxygen saturation measurements at the measurement site. The hemoglobin oxygen saturation measurements made at the measurement site are then analyzed. One of i) making the hemoglobin oxygen saturation measurements and ii) analyzing the hemoglobin oxygen saturation measurements is performed in response to the detected first pulsatile characteristic.
Another embodiment of the invention is directed to a system for making measurement of hemoglobin oxygen saturation of a patient at a measurement site. The system includes means for detecting a pulsatile characteristic of the patient proximate the measurement site and means for making hemoglobin oxygen saturation measurements at the measurement site. The system also includes means for analyzing the hemoglobin oxygen saturation measurements made at the measurement site. One of i) the means for making the hemoglobin oxygen saturation measurements and ii) the means for analyzing the hemoglobin oxygen saturation measurements responds to the detected pulsatile characteristic.
Another embodiment of the invention is directed to an apparatus for measuring oxygen saturation of hemoglobin at a measurement site on a patient. The apparatus includes a controller having a first input to receive a first pulsatile input signal based on a first pulsatile patient characteristic measured proximate the measurement site, a first output to control making hemoglobin oxygen saturation measurements and a second input to receive signals related to the measurements of oxygen saturation of hemoglobin made at the measurement site. The controller includes a processor that i) controls making the hemoglobin oxygen saturation measurements or ii) analyzes the received signals in response to the detected first pulsatile characteristic.
Another embodiment of the invention is directed to a sensor unit for making measurements of hemoglobin oxygen saturation on a patient. The sensor unit includes a body attachable to the patient. The body has one or more optical ports for delivering light to the patient at first and second wavelengths for measuring hemoglobin oxygen saturation. At least a portion of a detector is mounted on the body to measure a pulsatile characteristic of the patient.
Another embodiment of the invention is directed to a method of determining hemoglobin oxygen saturation at a measurement site on a patient. The method includes measuring a first pulsatile characteristic arising from contraction of the patient""s heart and illuminating the measurement site with light at two different wavelengths. Light at the two different wavelengths is detected at the measurement site to produce detection signals. The detection signals are analyzed to determine hemoglobin oxygen saturation levels at the measurement site. One of i) illuminating the measurement site and ii) analyzing the detected light is performed in response to the measured first pulsatile characteristic.
Another embodiment of the invention is directed to a system for determining hemoglobin oxygen saturation at a measurement site on a patient. The system includes means for measuring a first pulsatile characteristic arising from contraction of the patient""s heart and means for illuminating the measurement site with light at two different wavelengths. The system also includes means for detecting the light at the two different wavelengths at the measurement site to produce detection signals and means for analyzing the detection signals to determine hemoglobin oxygen saturation levels at the measurement site. One of i) the means for illuminating the measurement site and ii) the means for analyzing the detected light performs in response to the measured first pulsatile characteristic.
Another embodiment of the invention is directed to a system for measuring oxygen saturation of hemoglobin at a measurement site on a patient. The invention includes a controller having a first input to receive a first pulsatile measurement signal, indicative of a first pulsatile characteristic resulting from contraction of the patient""s heart, from the patient, a first output to control making hemoglobin oxygen saturation measurements and a second input to receive signals related to the measurements of oxygen saturation of hemoglobin made at the measurement site. The controller also includes a processor that i) controls making the hemoglobin oxygen saturation measurements or ii) analyzes the received signals in response to the received first pulsatile measurement signal.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.